The invention pertains to a chemical-mechanical abrasive composition and method. The chemical-mechanical abrasive composition is useful in polishing the surface of a semiconductor wafer.
Chemical-mechanical polishing (CMP) is a planarization technique which was developed to address the problem associated with the difficulty in focusing during a photolithography process for producing integrated circuits due to the difference in the thickness of deposited films. The chemical-mechanical polishing technique was first applied to the production of the elements with a size in the order of 0.5 microns. With the reduction in the size of elements, the chemical-mechanical polishing technique was applicable to an creased number of layers. Until the elements were developed to be in the order of 0.25 microns, the chemical-mechanical polishing became an important and essential planarization technique. In general, the polishing method for producing a wire circuit comprises mounting a semiconductor wafer on a spinning platen equipped with an abrasive head and applying an abrasive slurry comprising abrasive particles and chemical additives to the surface of the wafer to enhance the abrasion performance. In fact, the CMP technique is the one which first modifies the surface to be polished by changing the chemical properties of the surface and then removes the modified surface in a mechanically abrasive manner.
During polishing methods, different chemical-mechanical abrasive slurries should be used with reference to different designs and production processes for various IC patterns. With respect to the polishing of a dielectric layer, commonly known or commercialized abrasive slurries are normally adjusted to be in the basic pH range, i.e. from 10 to 11.5, so as to enhance the removal rate of the dielectric layer. Alternatively, using CeO2 or Si3N4 particles to enhance the abrasion rate was previously taught. For example, EP 0 786 504 A2 discloses a polishing composition having a high selectivity for polishing silicon dioxide relative to silicon nitride, said composition comprising silicon nitride particles, water and an acid. U.S. Pat. No. 5,759,917 discloses a chemical-mechanical polishing composition and method for polishing silicon dioxide and silicon nitride in the production of semiconductors and integrated circuits. The composition of U.S. Pat. No. 5,759,917 has a high selectivity for polishing silicon dioxide relative to silicon nitride and comprises a salt, a soluble cerium, and a carboxylic acid, and has a pH ranging from 3 to 11. U.S. Pat. No. 5,861,054 discloses a polishing composition for use in polishing silicon dioxide and silicon nitride with a high selectivity for silicon dioxide relative to silicon nitride, which composition comprises an acidic solvent and silicon nitride with a primary particle size in the range of from 0.01 to 1000 nm. U.S. Pat. No. 5,891,205 discloses a chemical-mechanical polishing composition for polishing semiconductor devices, which composition comprises an alkaline aqueous dispersion that contains mixed particles of cerium oxide and silicon dioxide. In yet another alternative, it has been previously taught to use harder Al2O3 abrasive particles to enhance the abrasion rate. For example, U.S. Pat. No. 5,084,071 discloses a method for polishing an electronic component substrate using of a chemical-mechanical polishing slurry, which polishing slurry comprises no more than 1 weight percent of alumina, abrasive particles (e.g. SiO2, CeO2, SiC, Si3N4, or Fe2O3 particles), a transition metal chelated salt (e.g. ammonium iron EDTA) for use as a polishing accelerator, and a solvent for said salt. U.S. Pat. No. 5,336,542 discloses a polishing composition comprising alumina abrasive particles and a chelating agent selected from the group consisting of polyaminocarboxylic acid (e.g. EDTA) and the sodium and potassium salts thereof. The composition of U.S. Pat. No. 5,336,542 may further comprise boehmite or an aluminum salt.
One object of the present invention is to provide a chemical-mechanical abrasive composition which can effectively enhance the removal rate of a dielectric layer in either an acidic or a basic medium. The materials which can be used as dielectrics include silicon dioxide, silicon nitride, borophosphosilicate glass (BPSG), and those having a low dielectric constant (low-k), and the composites thereof. It has been discovered that the chemical-mechanical abrasive composition of the present invention is also effective in polishing polysilicon.
In the polishing method for semiconductor devices, as shown in FIG. 1, a chemical-mechanical polishing slurry should be used to planarize the silicon dioxide layer and stop at the silicon nitride layer. The removal rate of silicon dioxide to silicon nitride should be at least greater than 3. Accordingly, another object of the present invention is to provide a chemical-mechanical abrasive composition for use in the polishing of semiconductor devices, which composition is able to provide a ratio of greater than 3 of the removal rate of silicon dioxide to that of silicon nitride.
As for the polishing of metals, for example, in the copper processes for producing semiconductors, the polishing method should involve several steps. In the first step, as shown in FIG. 2(a), an abrasive slurry is used to polish the copper film of a semiconductor and stops at the tantalum nitride (TaN) layer, wherein the ratio of the removal rate of the copper film to that of the tantalum nitride layer should be at least greater than 3. In the second step, as shown in FIG. 2(b), another abrasive slurry is used to polish the tantalum nitride layer and the copper film of the semiconductor and stops at a dielectric layer, wherein the ratio of the removal rate of the tantalum nitride layer to that of the copper film should be at least greater than 1. Since in the first and second steps, the copper film may be subjected to a dishing phenomenon, a third step of over-polishing, as shown in FIG. 2(c), may be needed. The third abrasive slurry used in the third step should achieve a removal rate of the dielectric layer that is greater than or the same as that of the copper film and tantalum nitride layer. The polishing technology for metals has been disclosed in prior patents. For example, U.S. Pat. No. 5,114,437 discloses a polishing composition for an aluminum substrate, said composition comprising an alumina polishing agent having an average particle size of 0.2 to 5 xcexcm, and a polishing accelerator selected from the group consisting of chromium(III) nitrate, lanthanium nitrate, ammonium cerium(III) nitrate, and neodymium nitrate. U.S. Pat. No. 5,209,816 discloses a method for polishing an Al- or Ti-containing metal layer with a chemical-mechanical abrasive slurry. The abrasive slurry contains, in addition to a solid abrasive material, about 0.1-20% by volume of H3PO4 and about 1-30% by volume of H2O2. U.S. Pat. No. 5,225,034 discloses a chemical-mechanical abrasive slurry, which comprises AgNO3, solid abrasive particles, and an oxidant selected from H2O2, HOCl, KOCl, KMgO4, or CH3COOOH. The slurry is used for polishing the copper layer on a semiconductor wafer so as to produce copper wires on the wafer. U.S. Pat. No, 5,340,370 discloses a chemical-mechanical polishing slurry for tungsten or tungsten nitride film, which comprises an oxidizing agent such as potassium ferricyanide, an abrasive, and water, and has a pH range between 2 and 4, U.S. Pat. No. 5,516,346 discloses a slurry for chemical mechanically polishing a titanium film, said slurry comprising potassium fluoride in a concentration sufficient to complex with said titanium film and an abrasive such as silica, and having a pH level less than 8.
Yet another object of the present invention is to provide a chemical-mechanical abrasive composition which can effectively improve the removal rate of metals. Depending on different IC pattern designs and different semiconductor processes, the chemical-mechanical composition of the invention can provide the sane or different abrasion selectivities to the metal wires and dielectric layers in integrated circuits.